1. Field of the Invention
The present invention relates to a coupling construction between an actuator and a base, and a linear actuator device using such a coupling construction.
2. Description of the Related Art
A rodless cylinder which has an internal moving body moving axially within a cylinder tube and an external moving body driven by the internal moving body through a axially extending slit on the wall of the cylinder tube is known in the art. A linear actuator using a rodless cylinder is also known. Generally, a linear actuator includes an elongated base on which a rodless cylinder is rigidly coupled, and a slide body driven by the rodless cylinder and moving back and forth on the base along a longitudinal axis of the base.
A linear actuator of this type is disclosed in various publications.
For example;
(A) Japanese Design registration Publication No. 798741 discloses a linear actuator in which a rodless cylinder is coupled to its base using L-shaped brackets.
More specifically, in the linear actuator of the '741 publication, an L-shaped bracket is provided on each of the end caps attached to either end of the rodless cylinder. The rodless cylinder is coupled rigidly to the base by fastening the L-shaped brackets to the base using mounting bolts. The mounting bolts are screwed into the base in a direction perpendicular to the upper face of the base in order to fasten the bracket to the base.
(B) Japanese Unexamined Patent Publication (Kokai) No. 8-210311 discloses a coupling construction between a rodless cylinder and a base using a T-shaped groove formed on the upper face of the base. In the '031 publication, grooves having a T-shaped cross section are formed on the upper face of the base at the portion where the rodless cylinder is to be mounted. The grooves extend in the direction along the longitudinal axis of the base. The rodless cylinder is fixed to the base by tightening mounting nuts to bolts disposed in the groove and projecting upwardly therefrom. In other words, the mounting nuts are screwed into the bolts from the direction perpendicular to the upper face of the base.
(C) Japanese Patent No. 2502856 and Japanese Unexamined Patent Publication (Kokai) No. 9-177717 discloses a linear actuator provided with a position sensor for detecting the position of the slide body. In these publications, a groove is formed on the side wall of the base for fitting the position sensor directly to the base.
(D) Japanese Unexamined Patent Publication (Kokai) No. 59-227351 also discloses a linear actuator provided with a position sensor. In this publication, a sensor rail for mounting the position sensor is attached to the side wall of the base. The sensor rail extends in the longitudinal direction of the base and is attached to the side wall of the base by fitting bolts screwed into the side wall from the transverse direction (i.e., the direction along the width of the base).
However, in the publication (A), since the mounting bolts are directly screwed into the base, the threads of the bolt holes formed on the base tend to deform or break due to the tightening force of the bolts when the base is made of relatively soft material such as aluminum alloy.
When deformation or breakage of the threads occurs, the rigid coupling between the rodless cylinder and the base is lost.
Further, in this type of the coupling construction, tapped holes for the mounting bolts must be formed on the upper face of the face perpendicularly thereto. This requires machining such as drilling and tapping from a vertical direction (i.e., the direction perpendicular to the upper face of the base). Therefore, if other machining works from the horizontal direction (i.e., the longitudinal direction or the transverse direction of the base) is required, for example, in order to form other tapped holes for mounting end plates at both longitudinal ends of the base, the base must be machined from two different directions. This increases the steps and setup time required for the machining of the base.
In the coupling construction in the publication (B), a pair of T-shaped grooves extending along the entire length of the base are required for coupling the rodless cylinder to the base. Since these grooves extend along the entire length of the upper face of the base, the strength and the rigidity of the base are significantly lowered by these grooves.
In the linear actuator of the publication (C), the sensor rail in the form of a groove is formed on the side wall of the base. Therefore, distortion of the base due to the difference in thickness may occur in the portion where the groove is formed when the base is formed by a drawing or extrusion process. Further, since the sensor rail is formed as an integral part of the base, a larger size die is required for forming the base by a drawing or an extrusion process.
In the linear actuator of the publication (D), the tapped hole for fitting the sensor rail must be machined from the transverse direction. Therefore, if the machining of the tapped hole is required for fitting the end plate, the base must be machined from two different directions (i.e., from the transverse direction and the longitudinal direction). This also increases the steps and setup time required for the machining of the base. Further, the length of the base varies in accordance with the purpose of usage of the linear actuator. Since the longitudinal distance between the tapped holes must be determined in accordance with the length of the base, the machining of the tapped hole for fitting the sensor rail in the publication (C) is complicated.